The present invention generally relates to vehicle attitude angle sensing, and more particularly, to low-cost attitude (e.g., roll) angle estimation using signal blending for use in a vehicle.
Automotive vehicles are increasingly employing safety-related devices that deploy in the event that the vehicle rolls over to provide added protection to the occupants of the vehicle. For example, upon detecting a vehicle rollover condition, a pop-up roll bar can be deployed such that, when activated, the roll bar further extends vertically outward to increase the height of support provided by the roll bar. Other controllable features may include actuating deployment of one or more air bags, such as front or side deployment air bags, or actuating a pretensioner to pretension a restraining device, such as a seat belt or safety harness, to prevent occupants of the vehicle from ejecting from the vehicle or colliding with the roof of the vehicle.
In the past, basic rollover sensors have been employed in automotive vehicles to measure the angular position of the vehicle from which a rollover condition can be determined. The basic rollover sensors have included the use of a pendulum normally hanging vertically downward due to the Earth""s gravitational force. Many basic automotive sensing devices are employed simply to monitor the angular position of the vehicle relative to a level ground horizontal position. As a consequence, the basic automotive vehicle rollover sensors have generally been susceptible to error when the vehicle travels around a turn or becomes airborne, in which case the Earth""s gravitational force, which the sensor relies on, may be overcome by other forces.
More recently, sophisticated rollover sensing approaches have been considered. One such approach considered for rollover and pitchover sensing requires the use of six sensors including three accelerometers and three angular rate sensors, also referred to as gyros, all of which are employed together for use in an inertial navigation system which tracks position and attitude of the vehicle. The three accelerometers generally provide lateral, longitudinal, and vertical acceleration measurements of the vehicle, while the three gyros measure pitch rate, roll rate, and yaw rate. In sensing a rollover condition, the system determines a vehicle roll angle. However, the more sophisticated conventional rollover sensing approaches generally require a large number of high-precision and expensive sensors. In addition, known sophisticated systems are often susceptible to cumulative drift errors, and therefore must be reset occasionally.
It should be appreciated that various other applications may require knowledge of an attitude angle of the vehicle as the vehicle maneuvers on the ground. For example, attitude angle estimators may be employed to provide a roll angle indication to the driver of the vehicle. In the past, attitude angle estimators have employed one or more accelerometers and an angular rate sensor for each axis of rotation of the vehicle. However, there exists the problem of how to combine angle-related information sensed by the accelerometer and angular rate sensor in order to obtain an overall attitude angle measurement. This is because each type of sensor generally has characteristic failings in the conventional applications. For example, the accelerometer-based attitude angle estimate is generally relatively noisy when the vehicle is traveling on a rough road surface, and may sustain large errors whenever the vehicle""s trajectory involves an inertial acceleration having a component perpendicular to the rotational axis under consideration. In addition, the angular rate sensor estimate, which is typically obtained by integrating the sensed angular rate signal, generally has a tendency to drift with an ever-increasing error due to unknown bias or offset in the sensed angular rate signal.
It is therefore desirable to provide for an attitude angle estimator that provides an estimation of the attitude angle of a vehicle and minimizes errors that may be present in automotive-grade sensors. It is also desirable to provide for an attitude angle estimator that combines sensed signals measuring vehicle dynamics to obtain an overall more accurate attitude angle estimation. It is further desirable to provide for a vehicle roll angle estimator that minimizes the effects of noise present in an accelerometer-based angle estimate, and minimizes errors present in an angular rate sensed signal.
In accordance with the teachings of the present invention, an attitude angle estimator and method of estimating attitude (e.g., roll) angle of a vehicle are provided for estimating the attitude angle. The attitude angle estimator employs an angular attitude rate sensor for sensing angular attitude rate of a vehicle and producing an output signal, a first accelerometer for sensing vertical acceleration of the vehicle and producing an output signal, and a second accelerometer for detecting horizontal (e.g., lateral) acceleration of the vehicle and producing an output signal. A controller determines an acceleration-based attitude angle as a function of the sensed vertical and horizontal accelerations, and further determines an attitude angle estimate as a function of the angular attitude rate and the acceleration-based attitude angle.
The method for estimating an attitude angle of a vehicle according to the present invention includes the steps of sensing angular attitude rate of the vehicle and producing an output signal, sensing vertical acceleration of the vehicle and producing an output signal, and sensing lateral acceleration of the vehicle and producing an output signal. The method also includes the step of determining an acceleration-based attitude angle as a function of the sensed vertical and lateral accelerations. The method further includes the step of determining an attitude angle estimate as a function of the sensed angular rate signal and the acceleration-based attitude angle.
These and other features, advantages and objects of the present invention will be further understood and appreciated by those skilled in the art by reference to the following specification, claims and appended drawings.